20640681 has 12 divisors (see below), whose sum is σ = 29872752. Its totient is φ = 13733496.

The previous prime is 20640679. The next prime is 20640713. The reversal of 20640681 is 18604602.

It is not a de Polignac number, because 20640681 - 2¹ = 20640679 is a prime.

It is a super-2 number, since 2×20640681² = 852075424287522, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20640181) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3330 + ... + 7236.

It is an arithmetic number, because the mean of its divisors is an integer number (2489396).

Almost surely, 2^20640681 is an apocalyptic number.

It is an amenable number.

20640681 is a deficient number, since it is larger than the sum of its proper divisors (9232071).

20640681 is a wasteful number, since it uses less digits than its factorization.

20640681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4500 (or 4497 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 20640681 is about 4543.2016244054. The cubic root of 20640681 is about 274.3098108248.

It can be divided in two parts, 20640 and 681, that added together give a triangular number (21321 = T₂₀₆).

The spelling of 20640681 in words is "twenty million, six hundred forty thousand, six hundred eighty-one".